Track the version-compatible config settings inside railties

Instead of forcing new applications to carry an initializer that just
switches things to what their default "should" be, we can handle it
internally.

The initializer is then only used by upgraders: it shows what the new
default would be (commented out), while their upgraded application
continues to operate as it did before.

Under this model, a multiply-upgraded application could accumulate
several new_framework_defaults_*.rb files, for each release series it
has traversed. A given release series only needs to generate the latest,
though, because we don't support `rails app:upgrade` while skipping
releases.

5 files changed, 52 insertions, 37 deletions

diff --git a/railties/lib/rails/application/configuration.rb b/railties/lib/rails/application/configuration.rb
index b0592151b7..027207bbb2 100644
--- a/railties/lib/rails/application/configuration.rb
+++ b/railties/lib/rails/application/configuration.rb
@@ -55,6 +55,34 @@ module Rails
         @read_encrypted_secrets          = false
       end
 
+      def load_defaults(target_version)
+        case target_version.to_s
+        when "5.0"
+          if defined?(action_controller)
+            action_controller.per_form_csrf_tokens = true
+            action_controller.forgery_protection_origin_check = true
+          end
+
+          ActiveSupport.to_time_preserves_timezone = true
+
+          if defined?(active_record)
+            active_record.belongs_to_required_by_default = true
+          end
+
+          self.ssl_options = { hsts: { subdomains: true } }
+
+        when "5.1"
+          load_defaults "5.0"
+
+          if defined?(assets)
+            assets.unknown_asset_fallback = false
+          end
+
+        else
+          raise "Unknown version #{target_version.to_s.inspect}"
+        end
+      end
+
       def encoding=(value)
         @encoding = value
         silence_warnings do
diff --git a/railties/lib/rails/generators/rails/app/app_generator.rb b/railties/lib/rails/generators/rails/app/app_generator.rb
index 442258c9d1..38830ba38f 100644
--- a/railties/lib/rails/generators/rails/app/app_generator.rb
+++ b/railties/lib/rails/generators/rails/app/app_generator.rb
@@ -371,6 +371,14 @@ module Rails
         end
       end
 
+      def delete_new_framework_defaults
+        # Sprockets owns the only new default for 5.1: if it's disabled,
+        # we don't want the file.
+        unless options[:update] && !options[:skip_sprockets]
+          remove_file "config/initializers/new_framework_defaults_5_1.rb"
+        end
+      end
+
       def delete_bin_yarn_if_skip_yarn_option
         remove_file "bin/yarn" if options[:skip_yarn]
       end
diff --git a/railties/lib/rails/generators/rails/app/templates/config/application.rb b/railties/lib/rails/generators/rails/app/templates/config/application.rb
index c0a0bd0a3e..d5d214052f 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/application.rb
+++ b/railties/lib/rails/generators/rails/app/templates/config/application.rb
@@ -22,6 +22,9 @@ Bundler.require(*Rails.groups)
 
 module <%= app_const_base %>
   class Application < Rails::Application
+    # Initialize configuration defaults for originally generated Rails version.
+    config.load_defaults <%= Rails::VERSION::STRING.to_f %>
+
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration should go into files in config/initializers
     # -- all .rb files in that directory are automatically loaded.
diff --git a/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults.rb.tt
deleted file mode 100644
index bd844f0503..0000000000
--- a/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults.rb.tt
+++ /dev/null
@@ -1,37 +0,0 @@
-# Be sure to restart your server when you modify this file.
-#
-# This file contains migration options to ease your Rails 5.0 upgrade.
-#
-<%- if options[:update] -%>
-# Once upgraded flip defaults one by one to migrate to the new default.
-#
-<%- end -%>
-# Read the Guide for Upgrading Ruby on Rails for more info on each option.
-<%- unless options[:api] -%>
-
-# Enable per-form CSRF tokens. Previous versions had false.
-Rails.application.config.action_controller.per_form_csrf_tokens = <%= options[:update] ? false : true %>
-
-# Enable origin-checking CSRF mitigation. Previous versions had false.
-Rails.application.config.action_controller.forgery_protection_origin_check = <%= options[:update] ? false : true %>
-<%- end -%>
-
-# Make Ruby 2.4 preserve the timezone of the receiver when calling `to_time`.
-# Previous versions had false.
-ActiveSupport.to_time_preserves_timezone = <%= options[:update] ? false : true %>
-<%- unless options[:skip_active_record] -%>
-
-# Require `belongs_to` associations by default. Previous versions had false.
-Rails.application.config.active_record.belongs_to_required_by_default = <%= options[:update] ? false : true %>
-<%- end -%>
-<%- unless options[:update] -%>
-
-# Configure SSL options to enable HSTS with subdomains. Previous versions had false.
-Rails.application.config.ssl_options = { hsts: { subdomains: true } }
-<%- end -%>
-<%- unless options[:skip_sprockets] -%>
-
-# Unknown asset fallback will return the path passed in when the given
-# asset is not present in the asset pipeline.
-Rails.application.config.assets.unknown_asset_fallback = <%= options[:update] ? true : false %>
-<%- end -%>
diff --git a/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_5_1.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_5_1.rb.tt
new file mode 100644
index 0000000000..5f5545c4c7
--- /dev/null
+++ b/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_5_1.rb.tt
@@ -0,0 +1,13 @@
+# Be sure to restart your server when you modify this file.
+#
+# This file contains migration options to ease your Rails 5.1 upgrade.
+#
+# Once upgraded flip defaults one by one to migrate to the new default.
+#
+# Read the Guide for Upgrading Ruby on Rails for more info on each option.
+<%- unless options[:skip_sprockets] -%>
+
+# Unknown asset fallback will return the path passed in when the given
+# asset is not present in the asset pipeline.
+# Rails.application.config.assets.unknown_asset_fallback = false
+<%- end -%>